Electron microscope specimen holder having means for heating the specimen



June 21, 1966 J. H. LUCAS 3,257,554

ELECTRON MICROSCOPE SPECIMEN HOLDER HAVING MEANS FOR HEATING THESPECIMEN Filed Aug. 12, 1963 United States Patent The present inventionrelates to specimen holders for use in electron microscopes, and inparticular to specimen holders of the type which comprise means forheating the specimen.

In specimen holders of this type, the heating of the specimen isconveniently performed by mounting the specimen in good thermal contactwith an electrically conducting support and passing a current throughthe support so as to heat up the support and heat the specimen byconduction. The current for the support is supplied along twoconductors, and a magnetic field will be induced adjacent theseconductors by the current flowing therein.

In the operation of the electron microscope an electron beam is passedthrough the specimen while it is being heated and the current isflowing, and the field induced by the current may deflect the electronbeam by an unpredictable amount.

In order to prevent the deflection of the electron beam by these fieldsit is known to shield the conductors so as to restrict the fields, butthis is not always convenient or possible in some designs of specimenholder.

The object of the present invention is to provide an improved specimenholder of the above type.

According to the present invention a specimen holder for use in anelectron microscope comprises a pair of jaw members extendinglongitudinally on opposite sides respectively ot'the electron beam axisand electrically insulated from each other, the jaw members beingchannelled to form a beam passage, a pair of clamp members supported bythe jaw members with each clamp member making electrical connection withone of the jaw members, lugs extending inwardly from each of the clampmembers, a metal mesh specimen support extending across the electronbeam path with opposite edges resting on and supported by the lugsrespectively, and means for passing an electrical current through theseries path formed by the clamp members, the jaw members and the meshsupport to heat a specimen resting on the mesh support. Preferably theelectric current is supplied to the series circuit by electrical supplyleads twisted together and extending from external supply terminalsthrough a passage defined in a metal body from which the pair of flangedjaw members extend longitudinally.

Preferably said support is a mesh of electrically conducting materialbetween the strands of which there is very good electrical and thermalcontact. The mesh may be cold-rolled, so as to produce the required goodcontact between the strands, or may be electro-deposited in the form ofa continuous mesh.

The support may be connected to the conductors so that it can easily beremoved for cleaning or replacement.

In order that the invention may be more readily understood referencewill now be made to the accompanying drawing, in which:

FIG. 1 is a side view sectioned on an axial plane of a specimen holderembodying the invention;

FIG. 2 is a side view of the specimen holder partly sectioned and viewedin the direction II in FIG. 1;

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FIG. 3 is an exploded view of the components of the lower part of thespecimen holder, and

FIG. 4 is a general view of an electron microscope illustrating thespecimen holder in its operative position.

With reference to FIGS. 1, 2 and 3, the specimen holder comprises ahollow metal body 1, on the lower end of which are supported two metaljaws 2, 3, adapted to hold a mesh 4 which acts as a support for thespecimen. The mesh is secured to the lower ends of the two jaws by meansof an integral assembly of twoclamps 5, 6 and a clamping ring 7 whichfits over the outer surfaces of the jaws. The inner surfaces of theclamps fit closely against the outer surfaces of the jaws so that as theassembly is pushed axially on to the jaws the clamps are secured inposition. The ends of the clamps are formed respectively with lugs 8, 9,which are forced towards the ends of the jaws and hold the mesh 4securely against the ends of the aws.

The jaws 2, 3 are spaced apart and are electrically insulated from eachother. The lower end of the body 1 is formed with a boss 11, and aninsulating washer 12 with a central aperture 13 is located over the endof the body. The boss 11 extends through the aperture 13 and engages ina circular recess provided by two semicircular recesses 14, 15 formed injaws 2, 3 respectively. The jaws 2, 3 are attached to the body 1 bymeans of studs 16 which are secured within recesses 17 by means of asuitable insulating adhesive. This construction ensures that the jawsare held firmly against the lower end of the body, are accuratelylocated and are insulated from the body and from each other. The jaws 2,3 are arcuate in cross-section and are reduced in width at their lowerends. The sides of the jaws are spaced apart by only a fraction of amillimetre, and the gap between the jaws across which the mesh 4 issecured is aligned with the hollow centre of the body 1. The jaws extendcoaxially with the body and are made as short as possible.

In order to insulate the lower ends of the jaws a flanged bushing 18 ofelectrically insulating material is located between the clamping ring 7and the clamps 5, 6 so that these clamps are insulated from each other.

The body 1 is formed with a longitudinally extending bore 19 which isclosed at its upper end by a terminal plug 21 and extends to the lowerend of the body. This bore 19 provides a location for a pair of flexibleconductors 22, 23 which are connected at their lower ends to jaws 2, 3respectively, and at their upper ends to terminals 24, 25 respectively.These conductors are insulated from each other and are twisted togetherclosely in spiral form.

The specimen holder is supported in a conical recess in a suitable framewhen in use in an electron microscope. The recess closely encloses thebody 1 which is provided with bars 26, 27 by which it may be removedfrom the frame.

The holder described above is adapted to be used in an electronmicroscope as illustrated diagrammatically in FIG. 4. The electronmicroscope comprises a hollow body 31 adapted to be evacuated, anelectron source 32, two electron lens systems 33, 34 and a fluorescentviewing screen 35. The specimen holder 36 is located between the twolens systems and is of the type described above. The specimen is mountedon the supporting mesh 4, and the beam of electrons 37 passes throughthe hollow body 1 of the holder and between the jaws 2, 3 to strike thespecimen on the mesh 4. The electron beam continues so as to strike thefluorescent screen 35 in the Well known manner.

If it is desired to heat the specimen on the mesh 4 the terminals 24, 25on the holder are connected to a source of current, and this currentflows along the conductors 22,

23 and the jaws 2, 3 and through the mesh 4 so as to heat the mesh andto heat the specimen by conduction. Since the conductors 22, 23 areclosely twisted together the magnetic field produced by the currentpassing along these conductors, and the electric field due to thevoltage between the conductors, are reduced to a minimum and have only anegligible effect on the electron beam asit passes through the hollowbody 1.

Fields will be induced between the jaws 2, 3 but since these jaws aremade as short as possible the fields are reduced to a minimum. Henceheating of the specimen does not cause any appreciable deflection of theelectron beam.

In order to ensure that there is good electrical conductivity betweenall the strands of the mesh 4 and between the mesh and the jaws, andthat there is good thermal conductivity between the mesh and thespecimen and the mesh and the jaws, the mesh is made as flat aspossible. This can be arranged either by forming the mesh by anelectro-deposition process, so that the strands are continuous, or bycold-rolling a mesh made by well known methods, so that the strands areforced together. Each of these operations ensures that the strands ofthe mesh are in close contact and that the strands cannot work loose.

As a result there is very good electrical and thermal contact betweenthe jaws and the mesh, and very good thermal contact between the meshand the specimen and the jaws. The nature of the electrical and thermalcontact will be constant, and, therefore, for a given current throughthe mesh the heat generated and the heat lost will be constant, and,therefore, the change in temperature of the specimen will be the same.

By using meshes made of different materials the temperature range of theholder can be varied. For example a range of 30-1450 C. can be obtainedusing a stainless steel mesh, and a range of 30120 C. can be obtainedusing a copper mesh. For higher temperature applications platinum ortungsten, for example, can be used for the material of the mesh.

What I claim is:

1. In an electron microscope a specimen holder assembly comprising apair of jaw members extending longitudinally on opposite sidesrespectively of the electron beam axis and electrically insulated fromeach other, surfaces on said jaw members defining longitudinalchannelling in each said member to form a beam passage, a

men support extending across the electron beam path with opposite edgesresting on and supported by said lugs respectively, and means forpassing an electrical current through the series path formed by theclamp members, the jaw members and the mesh support to heat a specimenresting on the mesh support.

2. In an electron microscope a specimen holder assembly comprising ahollow metal body encircling the electron beam path, a pair of flangedjaw members extending longitudinally from said metal body on oppositesides respectively of the electron beam axis, said jaw members beingelectrically insulated from each other and from the metal body, surfaceson said jaw members defining longitudinal channelling in said members todefine a beam passage, a pair of clamp members supported by said jawmembers and each clamp member making electrical connection with one ofsaid jaw members, lugs extending inwardly from each of said clampmembers, a metal mesh specimen support extending across the electronbeam path with opposite edges resting on said lugs respectively, meansdefining a longitudinal passage in the wall of said metal body,electrical supply leads twisted together and extending from externalsupply terminals through said passage to respective jaw members, andmeans for passing electric current through the series circuit formed bythe clamp members, the jaw members, the mesh support and the electricalsupply leads.

References Cited by the Examiner UNITED STATES PATENTS 2,266,082 12/1941Ruska 250-495 2,423,158 7/1947 Runge 25049.5 2,753,458 7/1956 Kazato etal 25049.5 3,151,241 9/1964 Hermann et al 25049.5

- FOREIGN PATENTS 1,130,615 5/1962 Germany.

730,203 5/ 1955 Great Britain.

RALPH G; NILSON, Primary Examiner.

H. S. MILLER, G. E. MATTHEWS, A. L. BIRCH,

Assistant Examiners.

1. IN AN ELECTRON MICROSCOPE A SPECIMEN HOLDER ASSEMBLY COMPRISING APAIR OF JAW MEMBERS EXTENDING LONGITUNDINALLY ON OPPOSITE SIDESRESPECTIVELY OF THE ELECTRON BEAM AXIS AND ELECTRICALLY INSULATED FROMEACH OTHER, SURFACES ON SAID JAW MEMBERS DEFINING LONGITUDINALCHANNELLING IN EACH SAID MEMBERS TO FORM A BEAM PASSAGE, A PAIR OF CLAMPMEMBERS SUPPORTED BY SAID JAW MEMBERS AND EACH CLAMP MEMBER MAKINGELECTRICAL CONNECTION WITH ONE OF SAID JAW MEMBERS, LUGS EXTENDINGINWARDLY FROM EACH OF SAID CLAMP MEMBERS, A METAL MESH SPECI-